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gvpr - Man Page

library for graph filtering


#include <graphviz/gvpr.h>

  /* If set, gvpr calls exit() on errors */
#define GV_USE_EXIT 1
  /* If set, gvpr stores output graphs in gvpropts */

typedef ssize_t (*gvprwr) (void*, const char *buf, size_t nbyte, void*);

typedef struct {
    Agraph_t** ingraphs;      /* NULL-terminated array of input graphs */
    int n_outgraphs;          /* if GV_USE_OUTGRAPH set, output graphs */
    Agraph_t** outgraphs;
    gvprwr out;               /* write function for stdout */
    gvprwr err;               /* write function for stderr */
    int flags;
} gvpropts;

extern int gvpr (int argc, char *argv[], gvpropts* opts);


The gvpr library allows an application to perform general-purpose graph manipulation and filtering based on an awk-like language. (For a more complete description of this language, see gvpr(1).)

The library has a single entry point: the gvpr() function. This provides a standard argc/argv interface, along with a structure to support in-core graphs, application print functions, along with additional options.

When called, gvpr() processes any flags provided in the argv array, and compiles the gvpr program to be run (provided either via the -f flag or as an item in argv). It then runs the program on each input graph. If opt->ingraphs is non-NULL, this is taken as a NULL-terminated array of in-core graphs to be used as input. Otherwise, the unprocessed elements of argv are taken to be the names of files containing graphs to be processed. (If none remain, gvpr will read from stdin.)

Normally, gvpr writes any output graph to stdout. However, if  the flag GV_USE_OUTGRAPH is set in opts->flags, the output graphs will be stored in an array pointed to be opts->outgraphs and the count will be stored in opts->n_outgraphs. In this case, the application must call agclose() on each output graph when it is done with it.

The application can override the default write functions for stdout and stderr using the out and err fields in opts. When called by gvpr, the second argument will point to a buffer of characters to be written, while the third argument provides the number of characters. The function should return the number of bytes actually written.

Return Values

Normally, gvpr returns 0 on success and non-zero if an error occurs. Any relevant error message will have been written to stderr or the application's opts->err function will have been called. If, however, GV_USE_EXIT is set in opts->flags, gvpr will call exit(3) in case of an error.

See Also

gvpr(1), awk(1), cgraph(3)


Emden Gansner (erg@research.att.com).


15 OCTOBER 2013